Field of the Invention
The invention relates to a power conversion technology and particularly relates to a power conversion apparatus capable of compensating for cable loss.
Description of Related Art
A power conversion apparatus is mainly used for converting a lowly-stable high input voltage supplied by the power company into a highly-stable low DC output voltage that is suitable for various electronic devices. Therefore, such power conversion apparatus is extensively applied to electronic devices, such as computers, office automation equipment, industrial control equipment, and communication equipment.
When the load end requires a greater power, the power conversion apparatus needs to provide a greater output current for use of the load. An operation state of the power conversion apparatus at this moment is called an overload operation. In the overload operation, the greater output current usually causes a voltage drop on the output line. As a result, the voltage provided to the load end may exceed the specification. This phenomenon is generally called cable loss.
In the current power conversion apparatus, some cable loss compensation mechanisms may be adopted to compensate for the voltage drop of the output voltage caused by cable loss during the overload operation. One of the common cable loss compensation methods is to determine the value of the output current by detecting the length of the turn-off period of a power switch so as to decide the compensation amount for the output voltage; and another is to dispose an output current detection circuit to directly detect the value of the output current so as to decide the compensation amount for the output voltage.
However, when the power conversion apparatus operates in a continuous conduction mode (CCM), the turn-off period is fixed and does not reflect the value of the output current. Therefore, the method of carrying out cable loss compensation according to the turn-off period of the power switch is only applicable to a power conversion apparatus operating in a discontinuous conduction mode (DCM).
On the other hand, the current detection mechanism of the general current detection circuit is to sample the output current and cause the sampled current to pass through a specific resistor, and then determine the value of the sampled current passing through the resistor by measuring the voltage across the resistor, so as to calculate the value of the output current according to the sampled current. Thus, the general output current detection method will cause additional power consumption.